[Xen-devel] [PATCH v2] xen: prevent PVH Dom0 from having pages with more than one ref

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

With the current implementation of the Dom0 domain builder a PVH Dom0
ends up with pages that have 2 references, which means they are not
freed when Dom0 balloons memory down. This leads to those pages
not being freed in guest_remove_page, so they are leaked and the
memory accounting between Xen and Dom0 differs, because Dom0 OS
actually thinks they are freed, but d->tot_pages is not decreased.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
---
Changes since v1:
 - Fix coding style.
 - Fix a second occurrence of the same issue.
 - Use paging_mode_translate instead of is_pvh_domain.
---
 xen/arch/x86/domain_build.c |   18 +++++++++++-------
 1 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/domain_build.c b/xen/arch/x86/domain_build.c
index ba42fc9..842ed5f 100644
--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -1137,10 +1137,13 @@ int __init construct_dom0(
                                     L1_PROT : COMPAT_L1_PROT));
         l1tab++;
 
-        page = mfn_to_page(mfn);
-        if ( (page->u.inuse.type_info == 0) &&
-             !get_page_and_type(page, d, PGT_writable_page) )
-            BUG();
+        if ( !paging_mode_translate(d) )
+        {
+            page = mfn_to_page(mfn);
+            if ( (page->u.inuse.type_info == 0) &&
+                 !get_page_and_type(page, d, PGT_writable_page) )
+                BUG();
+        }
     }
 
     if ( is_pv_32on64_domain(d) )
@@ -1300,9 +1303,10 @@ int __init construct_dom0(
         if ( get_gpfn_from_mfn(mfn) >= count )
         {
             BUG_ON(is_pv_32bit_domain(d));
-            if ( !page->u.inuse.type_info &&
-                 !get_page_and_type(page, d, PGT_writable_page) )
-                BUG();
+            if ( !paging_mode_translate(d) )
+                if ( !page->u.inuse.type_info &&
+                     !get_page_and_type(page, d, PGT_writable_page) )
+                    BUG();
 
             dom0_update_physmap(d, pfn, mfn, vphysmap_start);
             ++pfn;
-- 
1.7.7.5 (Apple Git-26)


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